Kahatagaha Graphite Lanka Limited Vein Graphite Underground Mine - Sri Lanka
Graphite
Location
Kahatagaha Mines are located in North Western Province of Sri Lanka at Maduragoda, Dodangaslanda in the Kurunegala District, approximately 90 km. from the capital city of Colombo
History
The graphite industry was nationalized in 1971 and the state graphite corporation was established in 1971 under the state industrial corporation Act No.49 of 1957.Earlier Sri Lanka has approximately 3000 graphite mines. But now only has few. The Corporation took over the running of three large mines previously operated by the private sector Bogala, Kahatagaha and Kolongaha which form the backbone of the industry. In 1979, the corporation was re-named “State Mining and Development Corporation” with expanded functions including the mining, processing and marketing of mineral commodities. With the establishment of corporation, the three mines Kahatagaha, Kolongaha, Walakatahena situated very close to each other were grouped together into a single mine and re-named it as Kahatagaha-Kolongaha mine. This resulted in an improvement of ventilation of mine and rationalization of the mining operations.
Geological settings
Mining is confined to the vein type deposit which occur as fissure infillings in the metamorphic rocks of the Precambrian. The deposit occur in swarms of veins within narrow zones in structurally weak rock such as the core of anticlinal structures (Dome) where fractures are common. The direction of veins are variable in any given area, the major veins tend to have two identifiable directions. East West trending graphite veins are common with offshoot following joint planes and minor fracture in the host rock. The deposit are mainly concentrated in anticlinal folds with a more or less North South direction Disseminated graphite occur as small thin flakes and scales seldom over half a centimeter in diameter, and is found in a great variety of rocks such as crystalline limestone and dolomite, garnetiferous gneisses, acid gneisses and garnet sillimanite gneisses and charnikites. Amount of these graphite is small and not economically important. But in quartz and pegmatite veins, the graphite flakes are usually thicker and larger but occurrence is rare.
Natural Graphite can categorized into three types,
- Vein graphite (Medium to High Carbon %)
- Amorphous graphite (Medium to High Carbon %)
- Flaky graphite (Low Carbon %)
About the deposit
Kahatagaha-Kolongaha is the world biggest crystalline graphite mine which contains above 95% pure Carbon. Geologists believe that deposits contain graphite as vein type until 2050ft depth from the surface. But still there didn’t has any conclusion exactly, how it forms as vein type. They are using zig zag method to extract graphite. The deposit existed in east west direction therefore the adits were established in North south direction. The major important of this mine is water springs are not occur. But from the water table, water is going to depth. Therefore they used pumps to remove water from the mining areas.
Beneath the earth surface the temperature is increasing gradually. Ventilation fans are used to decrease the high temperature in the mining area. Also to supply current for the underground they are using high tension lines. So many methods are being using to mine graphite such as cut and fill method, stopping method etc. Mining is going on under 1132ft and 2000ft beneath the earth surface. Until 1132ft vertical shaft used to travel. But 1132ft-2000ft they used “Vinchi box” to travel. It is risky method for travelling to underground. Therefore the 2nd shaft is developing until 2000ft these days.
Diamond drilling machines are using to identify the graphite deposit. After that using dynamites they blast the area which contains graphite and extract them. Then they transport them near to the lift using trolleys.
Graphite Processing
After the mining graphite are sorted into different particle sizes by using a rotary screen called trommel. Larger particles are manually sorted by male and female workers. This sorting is very much important for the process of curing and grinding. The impurities associated with graphite separated in the curing section and categorized into different groups according to carbon cantent,- “Pitty” lump (totally dust) - 99% carbon.
- Hard lump - 97% carbon.
- Bright lump - 94% carbon
Using pulverizing machine particle sizes are decreasing up to 6mm – 150 microns range. Sieves are changing according to the grade. If the customer wants more flat graphite, flake machine is use for that. Finally the output product fill to the bags called jumbo bags for the shipment. Japan, USA, UK and Singapore are the major customers of graphite.
In the Research and development section of Kahatagaha graphite mainly testing,
- C content
- Volatility
- Moisture content
- Bulk Density
Furnace is used for test the C content
- 5g crucible used for this.
- First measure the weight of crucible (m1)
- Then measure the weight of graphite+crucible
- Heat it in the furnace under 10000C 4hrs
- C removed from graphite as CO2
- Finally measure the weight of crucible+residues and subtract the crucible weight
- Calculate the C % according to the weight
Also these days Kahatagaha R&D section try out to make a crucible using graphite. For that as a binding material they have used clay (Ball clay) and to get the thermal resistance Borosilicate.
Uses
- Carbon brushes
- Refractories
- Electrodes for electric arc furnaces
- Crucibles for continuous casting lubricants
- Lubricants
- Friction materials
- Graphite foil
- Anode material in lithium-ion batteries
- Moderate in nuclear reactors
- Carbon-Carbon composites
- Pencils
- Carbon-nano application